LOWER CAMBRIAN CAMBROCLAVES (INCERTAE-SEDIS) FROM XINJIANG, CHINA, WITH COMMENTS ON THE MORPHOLOGICAL VARIABILITY OF SCLERITES

Four species of cambroclave, an enigmatic group whose position within the Metazoa is unresolved, are described from the Lower Cambrian Yurtu s Formation of western Xinjiang, China. Cambroclavus bicornis is simil ar to a number of previously described species, including C. absonus f rom approximately equivalent age strata of South Australia. As in many cambroclave taxa, morphological variability of individual sclerites a ppears to be considerable. Morphometric analysis of four populations o f C. bicornis, using elliptic Fourier shape analysis (EFA), demonstrat es that this technique offers considerable discriminatory power. Two s amples from the upper parts of one section (Sugaitbulak) show morpholo gical stasis. They are also readily distinguishable from two other sam ples, which although from near-equivalent horizons in adjacent section s on Yurtus Mountain differ significantly from one another. Zhijinites claviformis is a robust sclerite, with a strongly ribbed spine. In co ntrast, Parazhijinites cf. guizhouensis has a remarkably slender spine , arising from a much reduced base. Finally, Wushichites minutus is mo re reminiscent of other Chinese cambroclaves, notably Deiradoclavus tr igonus, with a sclerite with a sub-circular base indented by a posteri or notch, and a much reduced spine. Although the overall morphology of cambroclaves appears to be related to protection from predatory attac k, the wide variation in basic sclerite types lacks convincing ecologi cal explanations.